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1.
用双剪法对小浪底砂岩在摩擦滑动中的电阻率变化进行了实验研究。结果表明,在摩擦滑动过程中,电阻率“趋势”变化有明显的方向性效应,在不同的测量方位上显示出较大的差异性和不同的前兆特征。平行于断层面的第Ⅰ道电阻率持续上升,大滑动前无明显异常反应;垂直横跨断层面两侧的第Ⅱ道随剪应力的增大电阻率由开始大幅度下降转为平稳变化,大滑动前出现清晰的突变异常,其幅值达50%左右;与断层面斜突成45°夹角的第Ⅲ道随剪应力的增大电阻率缓慢上升,达到某一极值后随块体的滑动转为下降。最后,本文简单地讨论了产生这些差异性现象的可能原因及其在地震预报中的应用。 相似文献
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在1.2千巴围压下进行了三种初始饱和岩样(辉长岩、花岗岩Ⅰ和Ⅱ,各以淡水和盐水饱和)的压缩实验直至破裂并继续到摩擦滑动,所有实验中测定了岩样电阻率。 以Brace等人研究表面电导的方法为基础,我们引入给定含水岩样的体电阻系数和面电导系数两个专用术语以分析实验结果。发现一旦岩样开始膨胀,其面电导系数随差应力增加都增大。结果表明:含水岩样体膨胀后电阻率下降主要是由于表面电导作用的增强。 和前人的结果不同,不同岩样摩擦滑动时电阻率变化各异。作者提出:这种差异可能与岩石中所含矿物颗粒大小有关。含大颗粒的岩石滑动时电阻率下降,而含小颗粒的岩石滑动时电阻率上升。 相似文献
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在岩石电阻率随压力变化的不同阶段,部份地减低轴向压力后再加压(每回总压降约为破坏应力的10%).研究这种特殊的加载方式下,即所谓应力反复对电阻率的影响.结果如下:(1)对高水饱和度岩石,随压力不断增加电阻率变化的总趋势为上升——平稳——下降的变化形态(包括饱和度为100——70%).对低饱和度岩石(实验中饱和度为70%和50%),电阻率变化的总趋势已改变.(2)对高饱和度岩石共作了十一次应力反复实验.除了水饱和度为71%的岩石在压力为30MPa 处,应力反复时电阻率无明显变化外,其余均呈现电阻率的负异常(下降幅度约2%左右),我国地电台在震前观测到的地电阻率变化以负异常为主.实验结果为解释这种负异常提供一种新的可能机制.(3)在电阻率随压力变化的下降段,特别是接近岩石破坏时,应力反复所引起的电阻率负异常与一般情况下出现的负异常相比,有以下三个特征:a)负异常的幅度要大一个数量级(约-20%);b)不仅应力下降时电阻率下降,而且应力恢复时电阻率仍然下降;c)各个方向电阻率变化的差别很大(约10%).以上这三个特征可作为岩石临近破坏的标志.而一般的电阻率负异常可能只与应力反复有关,并不意味着岩石处于临近破裂的危险状态.(4)低饱和度岩石,应力反复可能引起电阻率的正异常.作者还用 相似文献
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This study investigates the effectiveness of direct current electrical resistivity as a tool for assessing ground water/surface water interactions within streams. This research has shown that patterns of ground water discharge can be mapped at the meter scale, which is important for understanding stream water quality and ecosystem function. Underwater electrical resistivity surveys along a 107-m stream section within the Burd Run Watershed in South Central Pennsylvania identified three resistivity layers: a resistive (100 to 400 Ωm) surface layer corresponding to the streambed sediments, a conductive (20 to 100 Ωm) middle layer corresponding to residual clay sediments, and a resistive (100 to 450 Ωm) bottom layer corresponding to the carbonate bedrock. Tile probing to determine the depth to the bedrock and resistivity test box analysis of augered sediment samples confirmed these interpretations of the resistivity data. Ground water seeps occurred where the resistivity data showed that the residual clays were thinnest and bedrock was closest to the streambed. Plotting the difference in resistivity between two surveys, one conducted during low-stage and the other during high-stage stream conditions, showed changes in the conductivity of the pore fluids saturating the sediments. Under high-stream stage conditions, the top layer showed increased resistivity values for sections with surface water infiltration but showed nearly constant resistivity in sections with ground water seeps. This was expressed as difference values less than 50 Ωm in the area of the seeps and greater than 50 Ωm change for the streambed sediments saturated by surface water. Thus, electrical resistivity aided in characterizing ground water discharge zones by detecting variations in subsurface resistivity under high- and low-stream stage conditions as well as mapping subsurface heterogeneities that promote these exchanges. 相似文献
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The properties of rock resitivity were studied under pressure, particularly with “stress reversal”, a procedure in which the
pressure applied was increased and decreased.
It was observed that, 1) With pressure increasing, the main feature of resistivity change was increase-steady-decrease for
high-saturation rock samples (saturation 70–100%). But the main feature for low-saturation samples was different. 2) In 10
out of 11 cases of “stress reversal” for high-saturation samples the resistivity droped (about 2%). Such drop could explain
the anomalies in geoelectricity terms, which are commonly observed before earthquakes in China. 3) It was also observed shortly
before rock failure that, a) the resistivity drops more dramatically (about 20%) during “stress reversal” period, which is
much more than ordinary drops. b) these drops occurred not only during stress decrease but also during stress increase. c)
Resistivity exhibits anisotropy: the resistivity along different directions may differ by 10%. These three features may indicate
that the rock is nearing failure, while ordinary resistivity drops are only connected with “stress reversal” and may not mean
the imminence of rock failure. 4) Resistivity increase was observed during the “stress reversal” period for low-saturation
rock samples.
The results mentioned above were explained with the effect of water flowing in and out of the cracks of rock. The temporary
factors which yield a reduction of the maximum main stress, may enhence the possibility of earthquake occurrence. 相似文献
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Three controlled experiments were conducted at the Oregon Graduate Institute (OGI) with the purpose of evaluating electrical resistance tomography for imaging underground processes associated with in-situ site assessment and remediation. The OGI facilities are unique: a double-wall tank 10 m square and 5 m deep, filled with river bottom sediments and instrumented for geophysical and hydrological studies. At this facility, liquid contaminants could be released into the confined soil at a scale sufficiently large to represent real-world physical phenomena.In the first test, images of electrical resistivity were made before and during a controlled spill of gasoline into a sandy soil. The primary purpose was to determine if electrical resistivity images could detect the hydrocarbon in either the vadose or saturated zone. Definite changes in electrical resistivity were observed in both the vadose and saturated soils. The effects were an increase in resistivity of as much as 10% above pre-release values. A single resistive anomaly was imaged, directly below the release point, principally within the vadose zone but extending below the phreatic surface. The anomaly remained identifiable in tomograms taken two days after the release ended with clear indications of lateral spreading along the water table.The second test involved electrical resistance measurements before, during, and after air sparging in a saturated soil. The primary purpose was to determine if the electrical images could be used to detect and delineate the extent of the zone influenced by sparging. The images showed an increase of about 20% in resistivity over background values within the sparged zone and the extent of the imaged zone agreed with that inferred from other information.Electrical resistivity tomography measurements were made under a simulated oil storage tank in the third test. Comparison of images taken before and during separate releases of brine and water showed effects of changes induced by the water or brine. The simulated leak and its location were imaged as a conductive anomaly centered near the point of origin and were observed to spread with time during the release. 相似文献
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Monitoring and modelling of pore water pressure changes and riverbank stability during flow events 总被引：1，自引：0，他引：1
Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometer‐piezometers at increasing depths in a riverbank of the Sieve River, Tuscany (central Italy), with the overall objective of investigating pore pressure changes in response to ?ow events and their effects on bank stability. The saturated/unsaturated ?ow was modelled using a ?nite element seepage analysis, for the main ?ow events occurring during the four‐year monitoring period. Modelling results were validated by comparing measured with computed pore water pressure values for a series of representative events. Riverbank stability analysis was conducted by applying the limit equilibrium method (Morgenstern‐Price), using pore water pressure distributions obtained by the seepage analysis. The simulation of the 14 December 1996 event, during which a bank failure occurred, is reported in detail to illustrate the relations between the water table and river stage during the various phases of the hydrograph and their effects on bank stability. The simulation, according to monitored data, shows that the failure occurred three hours after the peak stage, during the inversion of ?ow (from the bank towards the river). A relatively limited development of positive pore pressures, reducing the effective stress and annulling the shear strength term due to the matric suction, and the sudden loss of the con?ning pressure of the river during the initial drawdown were responsible for triggering the mass failure. Results deriving from the seepage and stability analysis of nine selected ?ow events were then used to investigate the role of the ?ow event characteristics (in terms of peak stages and hydrograph characteristics) and of changes in bank geometry. Besides the peak river stage, which mainly controls the occurrence of conditions of instability, an important role is played by the hydrograph characteristics, in particular by the presence of one or more minor peaks in the river stage preceding the main one. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Cyclic shear response of channel-fill Fraser River Delta silt 总被引：2，自引：0，他引：2
The cyclic shear response of a channel-fill, low-plastic silt was investigated using constant-volume direct simple shear testing. Silt specimens, initially consolidated to stress levels at or above the preconsolidation stress, displayed cyclic-mobility-type strain development during cyclic loading without static shear stress bias. Liquefaction in the form of strain softening accompanied by loss of shear strength did not manifest regardless of the applied cyclic stress ratio, or the level of induced excess pore water pressure, suggesting that the silt is unlikely to experience flow failure under cyclic loading. The cyclic shear resistance of the silt increased with increasing overconsolidation ratio (OCR) for OCR>1.3. The silt specimens that experienced high equivalent excess cyclic pore water pressure ratios (ru>80%) resulted in considerable volumetric strains (2.5%–5%) during post-cyclic reconsolidation implying potentially significant changes to the particle fabric under cyclic loading. 相似文献
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在野外原地对某些自然状态非饱和的土层及含裂隙矽化灰岩电阻率随应变的变化进行了实验.主要结果有:1)低应力下,随体积的压缩电阻率下降;体积膨胀时电阻率上升;2)所测岩、土层电阻率相对变化(/)对微小应变()的变化响应甚为敏感,裂隙岩层比土层更甚.放大系数(/)/与应变量有关,对10-4应变通常有一、二百倍,对10-5应变可达数百乃至上千倍;3)电阻率相对变化幅度随力源强度和尺度的增加而增加,随力源距离的增加而衰减.电阻率变化起始时间随距离的增加显示出滞后现象;4)水平各向同性土层,在应力作用下,不同方向电阻率变化不同,呈现出方向性.通常垂直最大压缩方向的电阻率 下降较多,平行方向的∥下降较小或略有上升,与压力呈45的45下降幅度介于中等.含裂隙矽化灰岩则不同,不同方向电阻率的变化不仅与压缩方向有关,而且还与裂隙方向有关.通常是∥下降较多.当压应力平行裂隙时, 也下降,但当压应力垂直裂隙时, 则明显上升. 相似文献
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Connection between earthquakes and deep fluids revealed by magnetotelluric imaging in Songyuan,China
Yu TANG Aihua WENG Yue YANG Shiwen LI Jianjun NIU Yanhui ZHANG Yabin LI Jianping LI 《中国科学:地球科学(英文版)》2021,64(1):161-176
Songyuan is the most earthquake prone area in northeast China.Since 2006,earthquakes have occurred in the area in the form of swarms,with a maximum magnitude of M_L5.8.There is much controversy about the cause of the Songyuan earthquakes.We attempted to determine the cause using a three-dimensional electrical conductivity structure inverted from a regional network of magnetotelluric data in the Songyuan area.The L-BFGS inversion method was applied,with a fullimpedance tensor data set used as the inversion input.Combined with an evaluation of the earthquake locations,the resistivity model revealed a northeast-oriented hidden fault running through the Songyuan earthquake area(SEA),which was speculated to be the preexisting Fuyu-Zhaodong Fault(FZF).Our resistivity model also found an apparent lithospheric low-resistivity anomaly beneath the earthquake area,which breached the high-resistivity lithospheric mantle and stalled at the base of the crust.A petrophysical analysis showed that this lower crustal low-resistivity anomaly was most likely attributed to hydrated partial melting,which could release water into the lower crust during later magma emplacements.While weakening the strength of the FZF,these ascending fluids also increased the pore pressure in the fault,further reducing the shear strength of the fault.Shear stress action(a fault strike component of the east-west regional compress),together with possible near-surface disturbances,may drive the fault to slip and trigger the earthquakes in Songyuan.It is possible that the continuous replenishment of fluids from the deeper mantle forces the Songyuan earthquakes into the form of swarms.We infer that the Songyuan earthquakes could be attributed to a combination of preexisting faults,regional stress,and deep fluids associated with plate subduction,and near surface disturbances might induce the earthquakes in advance.The Songyuan earthquakes are inherently induced earthquakes,fed by deep fluids. 相似文献
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Ultrasonic Velocities, Acoustic Emission Characteristics and Crack Damage of Basalt and Granite 总被引：2，自引：0，他引：2
Acoustic emissions (AE), compressional (P), shear (S) wave velocities, and volumetric strain of Etna basalt and Aue granite were measured simultaneously during triaxial compression
tests. Deformation-induced AE activity and velocity changes were monitored using twelve P-wave sensors and eight orthogonally polarized S-wave piezoelectric sensors; volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the
rock surface. P-wave velocity in basalt is about 3 km/s at atmospheric pressure, but increases by > 50% when the hydrostatic pressure is
increased to 120 MPa. In granite samples initial P-wave velocity is 5 km/s and increases with pressure by < 20%. The pressure-induced changes of elastic wave speed indicate
dominantly compliant low-aspect ratio pores in both materials, in addition Etna basalt also contains high-aspect ratio voids.
In triaxial loading, stress-induced anisotropy of P-wave velocities was significantly higher for basalt than for granite, with vertical velocity components being faster than
horizontal velocities. However, with increasing axial load, horizontal velocities show a small increase for basalt but a significant
decrease for granite. Using first motion polarity we determined AE source types generated during triaxial loading of the samples.
With increasing differential stress AE activity in granite and basalt increased with a significant contribution of tensile
events. Close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly.
A concomitant increase of double-couple events indicating shear, suggests shear cracks linking previously formed tensile cracks. 相似文献
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在单轴压缩下,对经过高温焙烧的含水辉长岩进行了轴向和径向电阻率变化以及体积应变的同时连续测量.结果表明,在完全饱和前的非弹性压缩阶段,电阻率随压应力增高而降低;在完全饱和的弹性压缩阶段,电阻率升高;在非弹性的体积膨胀阶段,电阻率继续上升.从Archie 公式出发,通过近似分析,导出了电阻率变化和体积应变的关系式.实验结果和近似分析定性上相附.本文的主要结果是发现含水岩样在膨胀阶段电阻率的升高,初步认为这是由于热开裂的张开,降低了饱和度的结果. 相似文献
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In the past, domestic and abroad scientific workers have done a large number of experiment researches on a great number of researches of experiment for the relationship between electrical resistivity change and the load stress on rock (Geoelectric Testing Group, Department of Geophysics, Peking University and Research Division, Seismological Brigade of Lanzhou, 1978; Zhang, 1981; Chen, et al, 1983; Zhao, et al, 1983; Zhang, Lu, 1983; Zhang, et al, 1985; Brace, Orange, 1968; Kurite, 1986; Teisseyre, 1989), such as imitating dynamic fracture of rock, frictional sliding course, and observing its resistivity change shape with a lot of experimental workssuch as simulating the dynamic course of crustal rocks fracturing and frictional slipping along the fracture surface, and observing its resistivity change shape with experiment. They found that, in the fracture process of rock under loading, not only its resistivity shape change notably, and its direction changes also very clearly, and therefore many scientific workers have shown strong interest in anisotropy of resistivity change, and have done some researches onfor it. 相似文献
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Evolution of the shear wave velocity during shaking modeled in centrifuge shaking table tests 总被引：2，自引：1，他引：1
Chung-Jung Lee Chung-Ru Wang Yui-Chen Wei Wen-Yi Hung 《Bulletin of Earthquake Engineering》2012,10(2):401-420
Two in-flight shear wave velocity measurement systems were developed to perform the subsurface exploration of shear wave velocity
in a centrifuge model. The bender elements test and the pre-shaking test used in the study provided reliable and consistent
shear wave velocity profiles along the model depth before and after shaking in the centrifuge shaking table tests. In addition,
the use of the bender elements measurement system particularly developed here allowed continuous examination of the evolution
of shear wave velocity not only during and after the shaking periods in the small shaking events but also during the dissipation
period of excess pore water pressure after liquefaction in the large shaking events. The test results showed that the shear
wave velocity at different values of excess pore water pressure ratio varied as the effective mean stress to the power of
0.27, to a first approximation. Consequently, a relationship between the shear wave velocity evolution ratio and the excess
pore water pressure ratio is proposed to evaluate the changes in shear wave velocity due to excess pore water generation and
dissipation during shaking events. This relation will assist engineers in determining the shear stiffness reduction ratio
at various ru levels when a sand deposit is subjected to different levels of earthquake shaking. 相似文献
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极端冰雪条件下的顺层岩质边坡滑移稳定性分析 总被引：1，自引：0，他引：1
推导了典型岩石边坡在极端冰雪条件下的滑移稳定系数的表达式;通过计算分析,揭示了岩石边坡滑移稳定系数随裂隙内水深、坡高、坡角、滑面倾角等因素变化的规律及与冻深的关系,并绘制岩石边坡滑移稳定系数与边坡几何要素之间的关系图。研究表明,当考虑极端冰雪灾害影响时,岩石边坡滑移稳定系数发生较为明显的变化：随裂隙饱水程度、坡面角、主滑面倾角的增加而降低,随主滑面抗剪强度的减小而降低;裂隙饱水程度越高、坡体高度越低、坡面角越小、主滑面倾角越大的边坡的滑移稳定系数,对裂隙冰冻胀力的反应越敏感。 相似文献